The goal of this proposal is to further understand how the mammalian auditory system, especially in learning impaired children, responds to and encodes speech stimuli under combined stresses of stimulus repetition and background noise. Specifically, auditory evoked potentials measuring activity from the cortex and brainstem of normal and learning impaired children will be compared to investigate whether abnormal neural encoding of speech signals under stresses of repetition and noise might underlie the perceptual deficits observed in some children with language based learning impairments. In vivo recording of auditory evoked potentials from the midbrain, thalamus and cortex of guinea pigs will allow detailed description of auditory encoding in the mammalian nervous system. By using identical stimuli and similar patterns of stimulation in both human and guinea pig experiments, human evoked responses will be better understood in terms of response characteristics of specific regions of the auditory pathway, as demonstrated by in vivo recordings. Additional knowledge of auditory sensitivity to these stresses may provide information useful for training of learning impaired subjects so that they may better perceive and discriminate sounds necessary for speech. Improved speech perception may subsequently affect speech production, reading and higher level cognitive function as well.